Epoxides are a class of compounds containing an oxarine ring, They are conventionally produced by epoxidation of olefinic compounds containing olefinic group, C═C. Processes for the epoxidation of liquid olefinic compounds, using both homogeneous and heterogeneous solid catalyst, have been described in the prior art.Epoxidation of Liquid Olefinic Compounds Using Homogeneous Catalysts.
U.S. Pat. No. 4,864,041 (1989) discloses a process for the homogeneous epoxidation reaction of an olefinic organic substrate, using transition metal-substituted polyoxomatallate catalyst, the transition metal used was Co, Mn, Cu, Fe, or Cr. According to U.S. Pat. No. 5,155,241 (1992) styrene oxide is prepared by reacting styrene and hydrogen peroxide in biphasic liquid system in the presence of a bis (tri-n-alkyltinoxy) molybdic acid and an inorganic anion. Another U.S. Pat. No. 5,223,613 (1993) discloses an olefin epoxidation process in which an olifinically unsaturated substrate is converted with an oxidizing agent in the presence of a catalytic amount of a bimetallic complex, each of the two metallic elements of which is selected from V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt. Another U.S. Pat. No. 5,510,516 (1996) discloses a process for epoxidation of unsaturated acrylates by contacting it with hydrogen peroxide or organic peracids in the presence of alkali metal molybdates or tungstates or heteropolyacid.
In all the prior art processes, since the catalyst is dissolved in the reaction mixture, the separation of the catalyst is difficult and the catalyst can not be reused in the process. Because of this a lot of undesirable waste is produced and also the cost of epoxide production is high hence there is a need for developing a heterogeneous solid catalyst, which can be separated from the reaction mixture simply by filtration and also can be reused in the process for several times. A few processes utilizing heterogeneous solid catalysts for the epoxidation of olefinic organic compounds have also been described in the prior art.
Epoxidation of Liquid Olefinic Compounds Using Heterogeneous Solid Catalysts
According to U.S. Pat. No. 5,319,114 (1994), olefins are converted to epoxides by reacting them with an organic peroxide in the presence of a heterogeneous catalysts comprised of a carbon molecular sieve containing transition metal from the group IVA, VA, VIA, and VIIA transition elements, such as Ti, W, Cr, V, Mo, Ni, or Re. However, there is always a high possibility of leaching out of transition metals from the solid catalyst during the epoxidation process, causing a loss of catalytic activity and/or selectivity and also making difficult the separation of the leached out components from the reaction mixture [Reference I. W. C. E. Arends and R. A. Sheldon, Applied Catalysis A: General. Volume 212, page 175-187, year 2001]
European patent 0568336A2 disclosed a process for producing an epoxide by contacting an olefin with hydrogen peroxide in the presence of a titanium silicate zeolite catalyst. A recent U.S. Pat. No. 6,194,591 (2001) also disclosed an olefin epoxidation process using a titanium zeolite catalyst modified with Pt, Pd, or Cu compound. However, since the titanium silicate zeolite catalysts are acidic in nature they also catalyse the epoxide isomerization and/or epoxide ring opening, thereby reducing the selectivity for the formation of epoxide in the epoxidation process over these catalysts. For example, the isomerization of styrene oxide over Ti containing zeolite catalyst is quite fast and hence phenyl acetaldehyde instead of styrene oxide is formed in the epoxidation reaction [European Patent 0,100,117A1 (1984); Z. Fu et al. Microporous and Mesoporous Materials, volume 29, page 351-359 and year 1999]. Because of the limitations of the solid catalysts used in the prior art processes, there is a practical need to develop a better solid catalyst having higher selectivity for epoxide in the epoxidation of styrene and other liquid olefinic compounds and also high catalytic activity.
U.S. Pat. No. 6,534,661 discloses a bimetallic, primarily Pt and Pd noble metals supported on titanium containing silica support for the epoxidation of organic compounds such as propylene using hydrogen and oxygen at elevated pressure of 500-2000 psig. In this disclosure, the presence of Pt, Pd and Ti is essential for the epoxidation to occur. In addition, the reaction is carried out in gas/liquid phase but at elevated pressures and the catalyst is prepared by impregnation of reduced Pd and Pt containing solution (by hydrogen) on the titanium containing zeolite support. After filtration of the impregnated mass and drying, it is further reduced in hydrogen at 250-300° C. for 10-20 hours. The process of this disclosure is expensive and complicated requiring heterogeneous deposition for formation of the catalyst, and elevated pressures during application for epoxidation.